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Which statement is correct when adsorpti...

Which statement is correct when adsorption of gas take place on metal surface?
(a) `delta H` becomes less negative with pregress of reaction.
(b) with progress of reaction the strength of residual forces increases.
(c) `NH_3` is adsorbed more than `N_2`.
(d) Equilibrium concentration of adsorbate increases with increase in temperature.

A

a,c

B

a,b

C

b,d

D

b,c

Text Solution

AI Generated Solution

The correct Answer is:
To solve the question regarding the correct statement when adsorption of gas takes place on a metal surface, we will analyze each option step by step. ### Step 1: Analyze Statement (a) **Statement (a):** `ΔH` becomes less negative with the progress of the reaction. - When a gas adsorbs onto a metal surface, the randomness (entropy) of the gas molecules decreases because they are confined to the surface. - Since the entropy decreases, `ΔS` is negative, and thus the term `-TΔS` becomes less negative (or more positive). - According to the Gibbs free energy equation, `ΔG = ΔH - TΔS`, if `-TΔS` becomes less negative, then `ΔH` must become less negative to maintain the relationship. - Therefore, this statement is **correct**. ### Step 2: Analyze Statement (b) **Statement (b):** With the progress of the reaction, the strength of residual forces increases. - As more gas molecules adsorb onto the surface, the forces acting on the adsorbed molecules do not necessarily increase in strength. Instead, the forces may become balanced. - The statement implies that the residual forces acting on the adsorbed molecules increase, which is not generally true. - Therefore, this statement is **incorrect**. ### Step 3: Analyze Statement (c) **Statement (c):** `NH3` is adsorbed more than `N2`. - `NH3` is a polar molecule, while `N2` is a non-polar molecule. - Polar molecules tend to have stronger intermolecular forces and thus are adsorbed more readily on surfaces compared to non-polar molecules. - Therefore, this statement is **correct**. ### Step 4: Analyze Statement (d) **Statement (d):** Equilibrium concentration of adsorbate increases with an increase in temperature. - Adsorption is generally exothermic, meaning that as temperature increases, the equilibrium concentration of adsorbate typically decreases. - This is because higher temperatures provide more kinetic energy to the molecules, making it harder for them to adhere to the surface. - Therefore, this statement is **incorrect**. ### Conclusion The correct statements are (a) and (c). ### Final Answer The correct statements when adsorption of gas takes place on a metal surface are: - (a) `ΔH` becomes less negative with the progress of the reaction. - (c) `NH3` is adsorbed more than `N2`.
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